/*
 * Copyright (c) 2014, 2022, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package jdk.jshell;

import com.sun.source.tree.AnnotationTree;
import com.sun.source.tree.AssignmentTree;
import com.sun.source.tree.ClassTree;
import com.sun.source.tree.CompilationUnitTree;
import com.sun.source.tree.ErroneousTree;
import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.IdentifierTree;
import com.sun.source.tree.ImportTree;
import com.sun.source.tree.MemberReferenceTree;
import com.sun.source.tree.MemberSelectTree;
import com.sun.source.tree.MethodInvocationTree;
import com.sun.source.tree.MethodTree;
import com.sun.source.tree.ModifiersTree;
import com.sun.source.tree.NewClassTree;
import com.sun.source.tree.Scope;
import com.sun.source.tree.Tree;
import com.sun.source.tree.Tree.Kind;
import static com.sun.source.tree.Tree.Kind.METHOD;
import com.sun.source.tree.TypeParameterTree;
import com.sun.source.tree.VariableTree;
import com.sun.source.tree.YieldTree;
import com.sun.source.util.SourcePositions;
import com.sun.source.util.TreePath;
import com.sun.source.util.TreePathScanner;
import com.sun.source.util.Trees;
import com.sun.tools.javac.api.JavacScope;
import com.sun.tools.javac.code.Flags;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.Symbol.CompletionFailure;
import com.sun.tools.javac.code.Symbol.VarSymbol;
import com.sun.tools.javac.code.Symtab;
import com.sun.tools.javac.code.Type;
import com.sun.tools.javac.code.Type.ClassType;
import com.sun.tools.javac.parser.Scanner;
import com.sun.tools.javac.parser.ScannerFactory;
import com.sun.tools.javac.parser.Tokens.Token;
import com.sun.tools.javac.parser.Tokens.TokenKind;
import com.sun.tools.javac.tree.JCTree;
import com.sun.tools.javac.util.Context;
import jdk.internal.shellsupport.doc.JavadocHelper;
import com.sun.tools.javac.util.Name;
import com.sun.tools.javac.util.Names;
import com.sun.tools.javac.util.Pair;
import jdk.jshell.CompletenessAnalyzer.CaInfo;
import jdk.jshell.TaskFactory.AnalyzeTask;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;
import java.util.function.Predicate;

import javax.lang.model.element.Element;
import javax.lang.model.element.ElementKind;
import javax.lang.model.element.Modifier;
import javax.lang.model.element.TypeElement;
import javax.lang.model.type.DeclaredType;
import javax.lang.model.type.TypeMirror;

import static jdk.internal.jshell.debug.InternalDebugControl.DBG_COMPA;

import java.io.IOException;
import java.net.URI;
import java.nio.file.DirectoryStream;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.FileVisitResult;
import java.nio.file.FileVisitor;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.function.BiConsumer;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

import static java.util.stream.Collectors.toCollection;
import static java.util.stream.Collectors.toSet;

import java.util.stream.Stream;
import java.util.stream.StreamSupport;

import javax.lang.model.SourceVersion;

import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.PackageElement;
import javax.lang.model.element.QualifiedNameable;
import javax.lang.model.element.RecordComponentElement;
import javax.lang.model.element.TypeParameterElement;
import javax.lang.model.element.VariableElement;
import javax.lang.model.type.ArrayType;
import javax.lang.model.type.ExecutableType;
import javax.lang.model.type.TypeKind;
import javax.lang.model.util.ElementFilter;
import javax.lang.model.util.Types;
import javax.tools.JavaFileManager.Location;
import javax.tools.StandardLocation;

import jdk.jshell.ExpressionToTypeInfo.ExpressionInfo;
import static jdk.jshell.Util.REPL_DOESNOTMATTER_CLASS_NAME;
import static jdk.jshell.SourceCodeAnalysis.Completeness.DEFINITELY_INCOMPLETE;
import static jdk.jshell.TreeDissector.printType;

import static java.util.stream.Collectors.joining;

import javax.lang.model.type.IntersectionType;

/**
 * The concrete implementation of SourceCodeAnalysis.
 * @author Robert Field
 */
class SourceCodeAnalysisImpl extends SourceCodeAnalysis {

    private static final Map<Path, ClassIndex> PATH_TO_INDEX = new HashMap<>();
    private static final ExecutorService INDEXER = Executors.newFixedThreadPool(1, r -> {
        Thread t = new Thread(r);
        t.setDaemon(true);
        t.setUncaughtExceptionHandler((thread, ex) -> ex.printStackTrace());
        return t;
    });

    private final JShell proc;
    private final CompletenessAnalyzer ca;
    private final List<AutoCloseable> closeables = new ArrayList<>();
    private final Map<Path, ClassIndex> currentIndexes = new HashMap<>();
    private int indexVersion;
    private int classpathVersion;
    private final Object suspendLock = new Object();
    private int suspend;

    SourceCodeAnalysisImpl(JShell proc) {
        this.proc = proc;
        this.ca = new CompletenessAnalyzer(proc);

        int cpVersion = classpathVersion = 1;

        INDEXER.submit(() -> refreshIndexes(cpVersion));
    }

    @Override
    public CompletionInfo analyzeCompletion(String srcInput) {
        MaskCommentsAndModifiers mcm = new MaskCommentsAndModifiers(srcInput, false);
        if (mcm.endsWithOpenToken()) {
            proc.debug(DBG_COMPA, "Incomplete (open comment): %s\n", srcInput);
            return new CompletionInfoImpl(DEFINITELY_INCOMPLETE, null, srcInput + '\n');
        }
        String cleared = mcm.cleared();
        String trimmedInput = Util.trimEnd(cleared);
        if (trimmedInput.isEmpty()) {
            // Just comment or empty
            return new CompletionInfoImpl(Completeness.EMPTY, srcInput, "");
        }
        CaInfo info = ca.scan(trimmedInput);
        Completeness status = info.status;
        int unitEndPos = info.unitEndPos;
        if (unitEndPos > srcInput.length()) {
            unitEndPos = srcInput.length();
        }
        int nonCommentNonWhiteLength = trimmedInput.length();
        String src = srcInput.substring(0, unitEndPos);
        switch (status) {
            case COMPLETE: {
                if (unitEndPos == nonCommentNonWhiteLength) {
                    // The unit is the whole non-coment/white input plus semicolon
                    String compileSource = src
                            + mcm.mask().substring(nonCommentNonWhiteLength);
                    proc.debug(DBG_COMPA, "Complete: %s\n", compileSource);
                    proc.debug(DBG_COMPA, "   nothing remains.\n");
                    return new CompletionInfoImpl(status, compileSource, "");
                } else {
                    String remain = srcInput.substring(unitEndPos);
                    proc.debug(DBG_COMPA, "Complete: %s\n", src);
                    proc.debug(DBG_COMPA, "          remaining: %s\n", remain);
                    return new CompletionInfoImpl(status, src, remain);
                }
            }
            case COMPLETE_WITH_SEMI: {
                // The unit is the whole non-coment/white input plus semicolon
                String compileSource = src
                        + ";"
                        + mcm.mask().substring(nonCommentNonWhiteLength);
                proc.debug(DBG_COMPA, "Complete with semi: %s\n", compileSource);
                proc.debug(DBG_COMPA, "   nothing remains.\n");
                return new CompletionInfoImpl(status, compileSource, "");
            }
            case DEFINITELY_INCOMPLETE:
                proc.debug(DBG_COMPA, "Incomplete: %s\n", srcInput);
                return new CompletionInfoImpl(status, null, srcInput + '\n');
            case CONSIDERED_INCOMPLETE: {
                // Since the source is potentually valid, construct the complete source
                String compileSource = src
                        + ";"
                        + mcm.mask().substring(nonCommentNonWhiteLength);
                proc.debug(DBG_COMPA, "Considered incomplete: %s\n", srcInput);
                return new CompletionInfoImpl(status, compileSource, srcInput + '\n');
            }
            case EMPTY:
                proc.debug(DBG_COMPA, "Detected empty: %s\n", srcInput);
                return new CompletionInfoImpl(status, srcInput, "");
            case UNKNOWN:
                proc.debug(DBG_COMPA, "Detected error: %s\n", srcInput);
                return new CompletionInfoImpl(status, srcInput, "");
        }
        throw new InternalError();
    }

    private Tree.Kind guessKind(String code) {
        return proc.taskFactory.parse(code, pt -> {
            List<? extends Tree> units = pt.units();
            if (units.isEmpty()) {
                return Tree.Kind.BLOCK;
            }
            Tree unitTree = units.get(0);
            proc.debug(DBG_COMPA, "Kind: %s -- %s\n", unitTree.getKind(), unitTree);
            return unitTree.getKind();
        });
    }

    //TODO: would be better handled through a lexer:
    private final Pattern JAVA_IDENTIFIER = Pattern.compile("\\p{javaJavaIdentifierStart}\\p{javaJavaIdentifierPart}*");

    @Override
    public List<Suggestion> completionSuggestions(String code, int cursor, int[] anchor) {
        suspendIndexing();
        try {
            return completionSuggestionsImpl(code, cursor, anchor);
        } catch (Throwable exc) {
            proc.debug(exc, "Exception thrown in SourceCodeAnalysisImpl.completionSuggestions");
            return Collections.emptyList();
        } finally {
            resumeIndexing();
        }
    }

    private List<Suggestion> completionSuggestionsImpl(String code, int cursor, int[] anchor) {
        code = code.substring(0, cursor);
        Matcher m = JAVA_IDENTIFIER.matcher(code);
        String identifier = "";
        while (m.find()) {
            if (m.end() == code.length()) {
                cursor = m.start();
                code = code.substring(0, cursor);
                identifier = m.group();
            }
        }
        code = code.substring(0, cursor);
        if (code.trim().isEmpty()) { //TODO: comment handling
            code += ";";
        }
        OuterWrap codeWrap = switch (guessKind(code)) {
            case IMPORT -> proc.outerMap.wrapImport(Wrap.simpleWrap(code + "any.any"), null);
            case CLASS, METHOD -> proc.outerMap.wrapInTrialClass(Wrap.classMemberWrap(code));
            default -> proc.outerMap.wrapInTrialClass(Wrap.methodWrap(code));
        };
        String requiredPrefix = identifier;
        return computeSuggestions(codeWrap, cursor, anchor).stream()
                .filter(s -> s.continuation().startsWith(requiredPrefix) && !s.continuation().equals(REPL_DOESNOTMATTER_CLASS_NAME))
                .sorted(Comparator.comparing(Suggestion::continuation))
                .toList();
    }

    private List<Suggestion> computeSuggestions(OuterWrap code, int cursor, int[] anchor) {
        return proc.taskFactory.analyze(code, at -> {
            SourcePositions sp = at.trees().getSourcePositions();
            CompilationUnitTree topLevel = at.firstCuTree();
            List<Suggestion> result = new ArrayList<>();
            TreePath tp = pathFor(topLevel, sp, code, cursor);
            if (tp != null) {
                Scope scope = at.trees().getScope(tp);
                Predicate<Element> accessibility = createAccessibilityFilter(at, tp);
                Predicate<Element> smartTypeFilter;
                Predicate<Element> smartFilter;
                Iterable<TypeMirror> targetTypes = findTargetType(at, tp);
                if (targetTypes != null) {
                    if (tp.getLeaf().getKind() == Kind.MEMBER_REFERENCE) {
                        Types types = at.getTypes();
                        smartTypeFilter = t -> {
                            if (t.getKind() != ElementKind.METHOD) {
                                return false;
                            }
                            ExecutableElement ee = (ExecutableElement) t;
                            for (TypeMirror type : targetTypes) {
                                if (type.getKind() != TypeKind.DECLARED)
                                    continue;
                                DeclaredType d = (DeclaredType) type;
                                List<? extends Element> enclosed =
                                        ((TypeElement) d.asElement()).getEnclosedElements();
                                for (ExecutableElement m : ElementFilter.methodsIn(enclosed)) {
                                    boolean matches = true;
                                    if (!m.getModifiers().contains(Modifier.ABSTRACT)) {
                                        continue;
                                    }
                                    if (m.getParameters().size() != ee.getParameters().size()) {
                                        continue;
                                    }
                                    ExecutableType mInst = (ExecutableType) types.asMemberOf(d, m);
                                    List<? extends TypeMirror> expectedParams = mInst.getParameterTypes();
                                    if (mInst.getReturnType().getKind() != TypeKind.VOID &&
                                        !types.isSubtype(ee.getReturnType(), mInst.getReturnType())) {
                                        continue;
                                    }
                                    for (int i = 0; i < m.getParameters().size(); i++) {
                                        if (!types.isSubtype(expectedParams.get(i),
                                                             ee.getParameters().get(i).asType())) {
                                            matches = false;
                                        }
                                    }
                                    if (matches) {
                                        return true;
                                    }
                                }
                            }
                            return false;
                        };
                    } else {
                        smartTypeFilter = el -> {
                            TypeMirror resultOf = resultTypeOf(el);
                            return Util.stream(targetTypes)
                                    .anyMatch(targetType -> at.getTypes().isAssignable(resultOf, targetType));
                        };
                    }

                    smartFilter = IS_CLASS.negate()
                                          .and(IS_INTERFACE.negate())
                                          .and(IS_PACKAGE.negate())
                                          .and(smartTypeFilter);
                } else {
                    smartFilter = TRUE;
                    smartTypeFilter = TRUE;
                }
                switch (tp.getLeaf().getKind()) {
                    case MEMBER_REFERENCE, MEMBER_SELECT: {
                        javax.lang.model.element.Name identifier;
                        ExpressionTree expression;
                        Function<Boolean, String> paren;
                        if (tp.getLeaf().getKind() == Kind.MEMBER_SELECT) {
                            MemberSelectTree mst = (MemberSelectTree)tp.getLeaf();
                            identifier = mst.getIdentifier();
                            expression = mst.getExpression();
                            paren = DEFAULT_PAREN;
                        } else {
                            MemberReferenceTree mst = (MemberReferenceTree)tp.getLeaf();
                            identifier = mst.getName();
                            expression = mst.getQualifierExpression();
                            paren = NO_PAREN;
                        }
                        if (identifier.contentEquals("*"))
                            break;
                        TreePath exprPath = new TreePath(tp, expression);
                        TypeMirror site = at.trees().getTypeMirror(exprPath);
                        boolean staticOnly = isStaticContext(at, exprPath);
                        ImportTree it = findImport(tp);
                        boolean isImport = it != null;

                        List<? extends Element> members = membersOf(at, site, staticOnly && !isImport && tp.getLeaf().getKind() == Kind.MEMBER_SELECT);
                        Predicate<Element> filter = accessibility;

                        if (isNewClass(tp)) { // new xxx.|
                            Predicate<Element> constructorFilter = accessibility.and(IS_CONSTRUCTOR)
                                .and(el -> {
                                    if (el.getEnclosingElement().getEnclosingElement().getKind() == ElementKind.CLASS) {
                                        return el.getEnclosingElement().getModifiers().contains(Modifier.STATIC);
                                    }
                                    return true;
                                });
                            addElements(membersOf(at, members), constructorFilter, smartFilter, result);

                            filter = filter.and(IS_PACKAGE);
                        } else if (isThrowsClause(tp)) {
                            staticOnly = true;
                            filter = filter.and(IS_PACKAGE.or(IS_CLASS).or(IS_INTERFACE));
                            smartFilter = IS_PACKAGE.negate().and(smartTypeFilter);
                        } else if (isImport) {
                            paren = NO_PAREN;
                            if (!it.isStatic()) {
                                filter = filter.and(IS_PACKAGE.or(IS_CLASS).or(IS_INTERFACE));
                            }
                        } else {
                            filter = filter.and(IS_CONSTRUCTOR.negate());
                        }

                        filter = filter.and(staticOnly ? STATIC_ONLY : INSTANCE_ONLY);

                        addElements(members, filter, smartFilter, paren, result);
                        break;
                    }
                    case IDENTIFIER:
                        if (isNewClass(tp)) {
                            Function<Element, Iterable<? extends Element>> listEnclosed =
                                    el -> el.getKind() == ElementKind.PACKAGE ? Collections.singletonList(el)
                                                                              : el.getEnclosedElements();
                            Predicate<Element> filter = accessibility.and(IS_CONSTRUCTOR.or(IS_PACKAGE));
                            NewClassTree newClassTree = (NewClassTree)tp.getParentPath().getLeaf();
                            ExpressionTree enclosingExpression = newClassTree.getEnclosingExpression();
                            if (enclosingExpression != null) { // expr.new IDENT|
                                TypeMirror site = at.trees().getTypeMirror(new TreePath(tp, enclosingExpression));
                                filter = filter.and(el -> el.getEnclosingElement().getKind() == ElementKind.CLASS && !el.getEnclosingElement().getModifiers().contains(Modifier.STATIC));
                                addElements(membersOf(at, membersOf(at, site, false)), filter, smartFilter, result);
                            } else {
                                addScopeElements(at, scope, listEnclosed, filter, smartFilter, result);
                            }
                            break;
                        }
                        if (isThrowsClause(tp)) {
                            Predicate<Element> accept = accessibility.and(STATIC_ONLY)
                                    .and(IS_PACKAGE.or(IS_CLASS).or(IS_INTERFACE));
                            addScopeElements(at, scope, IDENTITY, accept, IS_PACKAGE.negate().and(smartTypeFilter), result);
                            break;
                        }
                        ImportTree it = findImport(tp);
                        if (it != null) {
                            // the context of the identifier is an import, look for
                            // package names that start with the identifier.
                            // If and when Java allows imports from the default
                            // package to the default package which would allow
                            // JShell to change to use the default package, and that
                            // change is done, then this should use some variation
                            // of membersOf(at, at.getElements().getPackageElement("").asType(), false)
                            addElements(listPackages(at, ""),
                                    it.isStatic()
                                            ? STATIC_ONLY.and(accessibility)
                                            : accessibility,
                                    smartFilter, result);
                        }
                        break;
                    case CLASS: {
                        Predicate<Element> accept = accessibility.and(IS_TYPE);
                        addScopeElements(at, scope, IDENTITY, accept, smartFilter, result);
                        addElements(primitivesOrVoid(at), TRUE, smartFilter, result);
                        break;
                    }
                    case BLOCK:
                    case EMPTY_STATEMENT:
                    case ERRONEOUS: {
                        boolean staticOnly = ReplResolve.isStatic(((JavacScope)scope).getEnv());
                        Predicate<Element> accept = accessibility.and(staticOnly ? STATIC_ONLY : TRUE);
                        if (isClass(tp)) {
                            ClassTree clazz = (ClassTree) tp.getParentPath().getLeaf();
                            if (clazz.getExtendsClause() == tp.getLeaf()) {
                                accept = accept.and(IS_TYPE);
                                smartFilter = smartFilter.and(el -> el.getKind() == ElementKind.CLASS);
                            } else {
                                Predicate<Element> f = smartFilterFromList(at, tp, clazz.getImplementsClause(), tp.getLeaf());
                                if (f != null) {
                                    accept = accept.and(IS_TYPE);
                                    smartFilter = f.and(el -> el.getKind() == ElementKind.INTERFACE);
                                }
                            }
                        } else if (isTypeParameter(tp)) {
                            TypeParameterTree tpt = (TypeParameterTree) tp.getParentPath().getLeaf();
                            Predicate<Element> f = smartFilterFromList(at, tp, tpt.getBounds(), tp.getLeaf());
                            if (f != null) {
                                accept = accept.and(IS_TYPE);
                                smartFilter = f;
                                if (!tpt.getBounds().isEmpty() && tpt.getBounds().get(0) != tp.getLeaf()) {
                                    smartFilter = smartFilter.and(el -> el.getKind() == ElementKind.INTERFACE);
                                }
                            }
                        } else if (isVariable(tp)) {
                            VariableTree var = (VariableTree) tp.getParentPath().getLeaf();
                            if (var.getType() == tp.getLeaf()) {
                                accept = accept.and(IS_TYPE);
                            }
                        }

                        addScopeElements(at, scope, IDENTITY, accept, smartFilter, result);

                        Tree parent = tp.getParentPath().getLeaf();
                        accept = switch (parent.getKind()) {
                            case VARIABLE -> ((VariableTree) parent).getType() == tp.getLeaf() ?
                                             IS_VOID.negate() :
                                             TRUE;
                            case PARAMETERIZED_TYPE -> FALSE; // TODO: JEP 218: Generics over Primitive Types
                            case TYPE_PARAMETER, CLASS, INTERFACE, ENUM, RECORD -> FALSE;
                            default -> TRUE;
                        };
                        addElements(primitivesOrVoid(at), accept, smartFilter, result);
                        break;
                    }
                }
            }
            anchor[0] = cursor;
            return result;
        });
    }

    private static final Set<Kind> CLASS_KINDS = EnumSet.of(
            Kind.ANNOTATION_TYPE, Kind.CLASS, Kind.ENUM, Kind.INTERFACE, Kind.RECORD
    );

    private Predicate<Element> smartFilterFromList(AnalyzeTask at, TreePath base, Collection<? extends Tree> types, Tree current) {
        Set<Element> existingEls = new HashSet<>();

        for (Tree type : types) {
            if (type == current) {
                return el -> !existingEls.contains(el);
            }
            existingEls.add(at.trees().getElement(new TreePath(base, type)));
        }

        return null;
    }

    @Override
    public SnippetWrapper wrapper(Snippet snippet) {
        return new SnippetWrapper() {
            @Override
            public String source() {
                return snippet.source();
            }

            @Override
            public String wrapped() {
                return snippet.outerWrap().wrapped();
            }

            @Override
            public String fullClassName() {
                return snippet.classFullName();
            }

            @Override
            public Snippet.Kind kind() {
                return snippet.kind() == Snippet.Kind.ERRONEOUS
                        ? ((ErroneousSnippet) snippet).probableKind()
                        : snippet.kind();
            }

            @Override
            public int sourceToWrappedPosition(int pos) {
                return snippet.outerWrap().snippetIndexToWrapIndex(pos);
            }

            @Override
            public int wrappedToSourcePosition(int pos) {
                return snippet.outerWrap().wrapIndexToSnippetIndex(pos);
            }
        };
    }

    @Override
    public List<SnippetWrapper> wrappers(String input) {
        return proc.eval.sourceToSnippetsWithWrappers(input).stream()
                .map(this::wrapper)
                .toList();
    }

    @Override
    public List<Snippet> sourceToSnippets(String input) {
        proc.checkIfAlive();
        List<Snippet> snl = proc.eval.toScratchSnippets(input);
        for (Snippet sn : snl) {
            sn.setId(Snippet.UNASSOCIATED_ID);
        }
        return snl;
    }

    @Override
    public Collection<Snippet> dependents(Snippet snippet) {
        return proc.maps.getDependents(snippet);
    }

    @Override
    public List<Highlight> highlights(String snippet) {
        if (snippet.isEmpty()) {
            snippet += ";";
        }
        //TODO: OuterWrap duplicated
        OuterWrap codeWrap = switch (guessKind(snippet)) {
            case IMPORT -> proc.outerMap.wrapImport(Wrap.simpleWrap(snippet + "any.any"), null);
            case CLASS, METHOD -> proc.outerMap.wrapInTrialClass(Wrap.classMemberWrap(snippet));
            default -> proc.outerMap.wrapInTrialClass(Wrap.methodWrap(snippet));
        };
        String wrappedCode = codeWrap.wrapped();
        return this.proc.taskFactory.analyze(codeWrap, task -> {
            List<Highlight> result = new ArrayList<>();
            CompilationUnitTree cut = task.cuTrees().iterator().next();
            Trees trees = task.trees();
            SourcePositions sp = trees.getSourcePositions();
            List<Token> tokens = new ArrayList<>();
            Scanner scanner = ScannerFactory.instance(new Context()).newScanner(wrappedCode, false);
            scanner.nextToken();
            BiConsumer<Integer, Integer> addKeywordForSpan = (spanStart, spanEnd) -> {
                int start = codeWrap.wrapIndexToSnippetIndex(spanStart);
                int end = codeWrap.wrapIndexToSnippetIndex(spanEnd);
                result.add(new Highlight(start, end, EnumSet.of(Attribute.KEYWORD)));
            };
            Consumer<Token> addKeyword = token -> addKeywordForSpan.accept(token.pos, token.endPos);
            while (scanner.token().kind != TokenKind.EOF) {
                Token token = scanner.token();

                tokens.add(token);
                switch (token.kind) {
                    case ABSTRACT, ASSERT, BOOLEAN, BREAK, BYTE, CASE, CATCH, CHAR, CLASS, CONST,
                         CONTINUE, DEFAULT, DO, DOUBLE, ELSE, ENUM, EXTENDS, FINAL, FINALLY, FLOAT,
                         FOR, GOTO, IF, IMPLEMENTS, IMPORT, INSTANCEOF, INT, INTERFACE, LONG,
                         NATIVE, NEW, PACKAGE, PRIVATE, PROTECTED, PUBLIC, RETURN, SHORT, STATIC,
                         STRICTFP, SUPER, SWITCH, SYNCHRONIZED, THIS, THROW, THROWS, TRANSIENT, TRY,
                         VOID, VOLATILE, WHILE, UNDERSCORE -> {
                        addKeyword.accept(token);
                    }
                }

                scanner.nextToken();
            }
            new TreePathScanner<Void, Void>() {
                @Override
                public Void visitIdentifier(IdentifierTree node, Void p) {
                    long start = sp.getStartPosition(cut, node);
                    long end = sp.getEndPosition(cut, node);
                    handleElement(false, start, end);
                    return super.visitIdentifier(node, p);
                }
                @Override
                public Void visitMemberSelect(MemberSelectTree node, Void p) {
                    long exprEnd = sp.getEndPosition(cut, node.getExpression());
                    Token ident = findTokensFrom(exprEnd, TokenKind.DOT, TokenKind.IDENTIFIER);
                    if (ident != null) {
                        handleElement(false, ident.pos, ident.endPos);
                    }
                    return super.visitMemberSelect(node, p);
                }
                @Override
                public Void visitClass(ClassTree node, Void p) {
                    ModifiersTree mods = node.getModifiers();
                    if (mods.getFlags().contains(Modifier.SEALED) ||
                        mods.getFlags().contains(Modifier.NON_SEALED)) {
                        List<Token> modifierTokens = new ArrayList<>();
                        long modsStart = sp.getStartPosition(cut, mods);
                        long modsEnd = sp.getEndPosition(cut, mods);
                        for (Token t : tokens) {
                            if (t.pos >= modsStart && t.endPos <= modsEnd) {
                                modifierTokens.add(t);
                            }
                        }
                        for (AnnotationTree at : mods.getAnnotations()) {
                            long annStart = sp.getStartPosition(cut, at);
                            long annEnd = sp.getEndPosition(cut, at);
                            modifierTokens.removeIf(t -> t.pos >= annStart && t.endPos <= annEnd);
                        }
                        OUTER: for (int i = 0; i < modifierTokens.size(); i++) {
                            if (modifierTokens.get(i).kind == TokenKind.IDENTIFIER) {
                                switch (modifierTokens.get(i).name().toString()) {
                                    case "non" -> {
                                        addKeywordForSpan.accept(modifierTokens.get(i).pos,
                                                                 modifierTokens.get(i + 2).endPos);
                                        break OUTER;
                                    }
                                    case "sealed" -> {
                                        addKeyword.accept(modifierTokens.get(i));
                                    }
                                }
                            }
                        }
                    }
                    int pos = ((JCTree) node).pos;
                    Token ident = switch (node.getKind()) {
                        case ANNOTATION_TYPE, INTERFACE ->
                            findTokensFrom(pos, TokenKind.INTERFACE, TokenKind.IDENTIFIER);
                        case CLASS -> findTokensFrom(pos, TokenKind.CLASS, TokenKind.IDENTIFIER);
                        case ENUM -> findTokensFrom(pos, TokenKind.ENUM, TokenKind.IDENTIFIER);
                        case RECORD -> {
                            Token recordCandidate = findTokensFrom(pos, TokenKind.IDENTIFIER);
                            if (recordCandidate != null && recordCandidate.name().contentEquals("record")) {
                                addKeyword.accept(recordCandidate);
                            }
                            yield findTokensFrom(pos, TokenKind.IDENTIFIER, TokenKind.IDENTIFIER);
                        }
                        default -> throw new IllegalStateException("Unsupported token kind: " + node.getKind());
                    };
                    if (ident != null) {
                        handleElement(true, ident.pos, ident.endPos);
                    }
                    if (!node.getPermitsClause().isEmpty()) {
                        long start = sp.getStartPosition(cut, node.getPermitsClause().get(0));
                        Token permitsCandidate = findTokensBefore(start, TokenKind.IDENTIFIER);
                        if (permitsCandidate != null && permitsCandidate.name().contentEquals("permits")) {
                            addKeyword.accept(permitsCandidate);
                        }
                    }
                    return super.visitClass(node, p);
                }
                @Override
                public Void visitMethod(MethodTree node, Void p) {
                    int pos = ((JCTree) node).pos;
                    Token ident = findTokensFrom(pos, TokenKind.IDENTIFIER);
                    if (ident != null) {
                        handleElement(true, ident.pos, ident.endPos);
                    }
                    return super.visitMethod(node, p);
                }
                @Override
                public Void visitVariable(VariableTree node, Void p) {
                    int pos = ((JCTree) node).pos;
                    if (sp.getEndPosition(cut, node.getType()) == (-1)) {
                        Token varCandidate = findTokensBefore(pos, TokenKind.IDENTIFIER);
                        if (varCandidate != null && "var".equals(varCandidate.name().toString())) {
                            addKeyword.accept(varCandidate);
                        }
                    }
                    Token ident = findTokensFrom(pos, TokenKind.IDENTIFIER);
                    if (ident != null) {
                        handleElement(true, ident.pos, ident.endPos);
                    }
                    return super.visitVariable(node, p);
                }
                @Override
                public Void visitYield(YieldTree node, Void p) {
                    long start = sp.getStartPosition(cut, node);
                    Token yield = findTokensFrom(start, TokenKind.IDENTIFIER);
                    addKeyword.accept(yield);
                    return super.visitYield(node, p);
                }
                @Override
                public Void visitErroneous(ErroneousTree node, Void p) {
                    for (Tree err : node.getErrorTrees()) {
                        scan(err, p);
                    }
                    return null;
                }
                @Override
                public Void scan(Tree tree, Void p) {
                    if (tree != null) {
                        long end = sp.getEndPosition(cut, tree);
                        if (end == (-1)) {
                            //synthetic
                            return null;
                        }
                    }
                    return super.scan(tree, p);
                }
                private void handleElement(boolean declaration, long codeStart, long codeEnd) {
                    Element el = trees.getElement(getCurrentPath());
                    if (getCurrentPath().getParentPath().getLeaf().getKind() == Kind.NEW_CLASS) {
                        NewClassTree nct = (NewClassTree) getCurrentPath().getParentPath().getLeaf();
                        if (nct.getIdentifier() == getCurrentPath().getLeaf()) {
                            el = trees.getElement(getCurrentPath().getParentPath());
                        }
                    }
                    if (el != null) {
                        boolean deprecated = task.getElements().isDeprecated(el);
                        if (declaration || deprecated) {
                            Set<Attribute> attributes = EnumSet.noneOf(Attribute.class);
                            if (declaration) {
                                attributes.add(Attribute.DECLARATION);
                            }
                            if (deprecated) {
                                attributes.add(Attribute.DEPRECATED);
                            }
                            int start = codeWrap.wrapIndexToSnippetIndex(codeStart);
                            int end = codeWrap.wrapIndexToSnippetIndex(codeEnd);
                            result.add(new Highlight(start, end, attributes));
                        }
                    }
                }
                private Token findTokensFrom(long pos, TokenKind... expectedKinds) {
                    int tokenIdx = 0;

                    while (tokenIdx < tokens.size() && tokens.get(tokenIdx).pos < pos) {
                        tokenIdx++;
                    }

                    if (tokenIdx + expectedKinds.length - 1 < tokens.size()) {
                        Token t = null;
                        for (TokenKind expectedKind : expectedKinds) {
                            t = tokens.get(tokenIdx);

                            if (t.kind != expectedKind) {
                                return null;
                            }

                            tokenIdx++;
                        }

                        return t;
                    }

                    return null;
                }
                private Token findTokensBefore(long pos, TokenKind... expectedKinds) {
                    int tokenIdx = 0;

                    while (tokenIdx < tokens.size() && tokens.get(tokenIdx).pos < pos) {
                        tokenIdx++;
                    }

                    tokenIdx--;

                    if (tokenIdx >= expectedKinds.length) {
                        Token t = null;
                        for (TokenKind expectedKind : expectedKinds) {
                            t = tokens.get(tokenIdx);

                            if (t.kind != expectedKind) {
                                return null;
                            }

                            tokenIdx--;
                        }

                        return t;
                    }

                    return null;
                }
            }.scan(cut, null);
            result.removeIf(h -> h.start() == h.end());
            Collections.sort(result, (h1, h2) -> h1.start() - h2.start());
            return result;
        });
    }

    private boolean isStaticContext(AnalyzeTask at, TreePath path) {
        switch (path.getLeaf().getKind()) {
            case ARRAY_TYPE:
            case PRIMITIVE_TYPE:
                return true;
            default:
                Element selectEl = at.trees().getElement(path);
                return selectEl != null && (selectEl.getKind().isClass() || selectEl.getKind().isInterface() || selectEl.getKind() == ElementKind.TYPE_PARAMETER) && selectEl.asType().getKind() != TypeKind.ERROR;
        }
    }

    private TreePath pathFor(CompilationUnitTree topLevel, SourcePositions sp, GeneralWrap wrap, int snippetEndPos) {
        int wrapEndPos = snippetEndPos == 0
                ? wrap.snippetIndexToWrapIndex(snippetEndPos)
                : wrap.snippetIndexToWrapIndex(snippetEndPos - 1) + 1;
        TreePath[] deepest = new TreePath[1];

        new TreePathScanner<Void, Void>() {
            @Override
            public Void scan(Tree tree, Void p) {
                if (tree == null)
                    return null;

                long start = sp.getStartPosition(topLevel, tree);
                long end = sp.getEndPosition(topLevel, tree);

                if (start <= wrapEndPos && wrapEndPos <= end &&
                    (deepest[0] == null || deepest[0].getLeaf() == getCurrentPath().getLeaf())) {
                    deepest[0] = new TreePath(getCurrentPath(), tree);
                    return super.scan(tree, p);
                }

                return null;
            }
            @Override
            public Void visitErroneous(ErroneousTree node, Void p) {
                return scan(node.getErrorTrees(), null);
            }
        }.scan(topLevel, null);

        return deepest[0];
    }

    private boolean isNewClass(TreePath tp) {
        return tp.getParentPath() != null &&
               tp.getParentPath().getLeaf().getKind() == Kind.NEW_CLASS &&
               ((NewClassTree) tp.getParentPath().getLeaf()).getIdentifier() == tp.getLeaf();
    }

    private boolean isThrowsClause(TreePath tp) {
        Tree parent = tp.getParentPath().getLeaf();
        return parent.getKind() == Kind.METHOD &&
                ((MethodTree)parent).getThrows().contains(tp.getLeaf());
    }

    private boolean isClass(TreePath tp) {
        return tp.getParentPath() != null &&
               CLASS_KINDS.contains(tp.getParentPath().getLeaf().getKind());
    }

    private boolean isTypeParameter(TreePath tp) {
        return tp.getParentPath() != null &&
               tp.getParentPath().getLeaf().getKind() == Kind.TYPE_PARAMETER;
    }

    private boolean isVariable(TreePath tp) {
        return tp.getParentPath() != null &&
               tp.getParentPath().getLeaf().getKind() == Kind.VARIABLE;
    }

    private ImportTree findImport(TreePath tp) {
        while (tp != null && tp.getLeaf().getKind() != Kind.IMPORT) {
            tp = tp.getParentPath();
        }
        return tp != null ? (ImportTree)tp.getLeaf() : null;
    }

    private Predicate<Element> createAccessibilityFilter(AnalyzeTask at, TreePath tp) {
        Scope scope = at.trees().getScope(tp);
        return el -> {
            switch (el.getKind()) {
                case ANNOTATION_TYPE: case CLASS: case ENUM: case INTERFACE: case RECORD:
                    return at.trees().isAccessible(scope, (TypeElement) el);
                case PACKAGE:
                case EXCEPTION_PARAMETER: case PARAMETER: case LOCAL_VARIABLE: case RESOURCE_VARIABLE:
                    return true;
                default:
                    TypeMirror type = el.getEnclosingElement().asType();
                    if (type.getKind() == TypeKind.DECLARED)
                        return at.trees().isAccessible(scope, el, (DeclaredType) type);
                    else
                        return true;
            }
        };
    }

    private final Predicate<Element> TRUE = el -> true;
    private final Predicate<Element> FALSE = TRUE.negate();
    private final Predicate<Element> IS_STATIC = el -> el.getModifiers().contains(Modifier.STATIC);
    private final Predicate<Element> IS_CONSTRUCTOR = el -> el.getKind() == ElementKind.CONSTRUCTOR;
    private final Predicate<Element> IS_METHOD = el -> el.getKind() == ElementKind.METHOD;
    private final Predicate<Element> IS_PACKAGE = el -> el.getKind() == ElementKind.PACKAGE;
    private final Predicate<Element> IS_CLASS = el -> el.getKind().isClass();
    private final Predicate<Element> IS_INTERFACE = el -> el.getKind().isInterface();
    private final Predicate<Element> IS_TYPE = IS_CLASS.or(IS_INTERFACE).or(el -> el.getKind() == ElementKind.TYPE_PARAMETER);
    private final Predicate<Element> IS_VOID = el -> el.asType().getKind() == TypeKind.VOID;
    private final Predicate<Element> STATIC_ONLY = el -> {
        ElementKind kind = el.getKind();
        Element encl = el.getEnclosingElement();
        ElementKind enclKind = encl != null ? encl.getKind() : ElementKind.OTHER;

        return IS_STATIC.or(IS_PACKAGE).or(IS_CLASS).or(IS_INTERFACE).test(el) || IS_PACKAGE.test(encl) ||
                (kind == ElementKind.TYPE_PARAMETER && !enclKind.isClass() && !enclKind.isInterface());
    };
    private final Predicate<Element> INSTANCE_ONLY = el -> {
        Element encl = el.getEnclosingElement();

        return IS_STATIC.or(IS_CLASS).or(IS_INTERFACE).negate().test(el) ||
                IS_PACKAGE.test(encl);
    };
    private final Function<Element, Iterable<? extends Element>> IDENTITY = Collections::singletonList;
    private final Function<Boolean, String> DEFAULT_PAREN = hasParams -> hasParams ? "(" : "()";
    private final Function<Boolean, String> NO_PAREN = hasParams -> "";

    private void addElements(Iterable<? extends Element> elements, Predicate<Element> accept, Predicate<Element> smart, List<Suggestion> result) {
        addElements(elements, accept, smart, DEFAULT_PAREN, result);
    }
    private void addElements(Iterable<? extends Element> elements, Predicate<Element> accept, Predicate<Element> smart, Function<Boolean, String> paren, List<Suggestion> result) {
        Set<String> hasParams = Util.stream(elements)
                .filter(accept)
                .filter(IS_CONSTRUCTOR.or(IS_METHOD))
                .filter(c -> !((ExecutableElement)c).getParameters().isEmpty())
                .map(this::simpleName)
                .collect(toSet());

        for (Element c : elements) {
            if (!accept.test(c))
                continue;
            if (c.getKind() == ElementKind.METHOD &&
                c.getSimpleName().contentEquals(Util.DOIT_METHOD_NAME) &&
                ((ExecutableElement) c).getParameters().isEmpty()) {
                continue;
            }
            String simpleName = simpleName(c);
            switch (c.getKind()) {
                case CONSTRUCTOR:
                case METHOD:
                    // add trailing open or matched parenthesis, as approriate
                    simpleName += paren.apply(hasParams.contains(simpleName));
                    break;
                case PACKAGE:
                    // add trailing dot to package names
                    simpleName += ".";
                    break;
            }
            result.add(new SuggestionImpl(simpleName, smart.test(c)));
        }
    }

    private String simpleName(Element el) {
        return el.getKind() == ElementKind.CONSTRUCTOR ? el.getEnclosingElement().getSimpleName().toString()
                                                       : el.getSimpleName().toString();
    }

    private List<? extends Element> membersOf(AnalyzeTask at, TypeMirror site, boolean shouldGenerateDotClassItem) {
        if (site  == null)
            return Collections.emptyList();

        switch (site.getKind()) {
            case INTERSECTION: {
                List<Element> result = new ArrayList<>();
                for (TypeMirror bound : ((IntersectionType) site).getBounds()) {
                    result.addAll(membersOf(at, bound, shouldGenerateDotClassItem));
                }
                return result;
            }
            case DECLARED: {
                TypeElement element = (TypeElement) at.getTypes().asElement(site);
                List<Element> result = new ArrayList<>();
                at.getElements().getAllMembers(element).forEach(m -> result.add(
                    element.equals(m.getEnclosingElement())
                        ? m
                        : (m instanceof Symbol.MethodSymbol ms)
                            ? ms.clone((Symbol)element)
                            : (m instanceof Symbol.VarSymbol vs)
                                ? vs.clone((Symbol)element)
                                : m));
                if (shouldGenerateDotClassItem) {
                    result.add(createDotClassSymbol(at, site));
                }
                result.removeIf(el -> el.getKind() == ElementKind.STATIC_INIT);
                return result;
            }
            case ERROR: {
                //try current qualified name as a package:
                TypeElement typeElement = (TypeElement) at.getTypes().asElement(site);
                Element enclosingElement = typeElement.getEnclosingElement();
                String parentPackageName = enclosingElement instanceof QualifiedNameable ?
                    ((QualifiedNameable)enclosingElement).getQualifiedName().toString() :
                    "";
                Set<PackageElement> packages = listPackages(at, parentPackageName);
                return packages.stream()
                               .filter(p -> p.getQualifiedName().equals(typeElement.getQualifiedName()))
                               .findAny()
                               .map(p -> membersOf(at, p.asType(), false))
                               .orElse(Collections.emptyList());
            }
            case PACKAGE: {
                String packageName = site.toString()/*XXX*/;
                List<Element> result = new ArrayList<>();
                result.addAll(getEnclosedElements(at.getElements().getPackageElement(packageName)));
                result.addAll(listPackages(at, packageName));
                return result;
            }
            case BOOLEAN: case BYTE: case SHORT: case CHAR:
            case INT: case FLOAT: case LONG: case DOUBLE:
            case VOID: {
                return shouldGenerateDotClassItem ?
                    Collections.singletonList(createDotClassSymbol(at, site)) :
                    Collections.emptyList();
            }
            case ARRAY: {
                List<Element> result = new ArrayList<>();
                result.add(createArrayLengthSymbol(at, site));
                if (shouldGenerateDotClassItem)
                    result.add(createDotClassSymbol(at, site));
                return result;
            }
            default:
                return Collections.emptyList();
        }
    }

    private List<? extends Element> membersOf(AnalyzeTask at, List<? extends Element> elements) {
        return elements.stream()
                .flatMap(e -> membersOf(at, e.asType(), true).stream())
                .toList();
    }

    private List<? extends Element> getEnclosedElements(PackageElement packageEl) {
        if (packageEl == null) {
            return Collections.emptyList();
        }
        //workaround for: JDK-8024687
        while (true) {
            try {
                return packageEl.getEnclosedElements()
                                .stream()
                                .filter(el -> el.asType() != null)
                                .filter(el -> el.asType().getKind() != TypeKind.ERROR)
                                .toList();
            } catch (CompletionFailure cf) {
                //ignore...
            }
        }
    }

    private List<? extends Element> primitivesOrVoid(AnalyzeTask at) {
        Types types = at.getTypes();
        return Stream.of(
                TypeKind.BOOLEAN, TypeKind.BYTE, TypeKind.CHAR,
                TypeKind.DOUBLE, TypeKind.FLOAT, TypeKind.INT,
                TypeKind.LONG, TypeKind.SHORT, TypeKind.VOID)
                .map(tk -> (Type)(tk == TypeKind.VOID ? types.getNoType(tk) : types.getPrimitiveType(tk)))
                .map(Type::asElement)
                .toList();
    }

    void classpathChanged() {
        synchronized (currentIndexes) {
            int cpVersion = ++classpathVersion;

            INDEXER.submit(() -> refreshIndexes(cpVersion));
        }
    }

    private Set<PackageElement> listPackages(AnalyzeTask at, String enclosingPackage) {
        synchronized (currentIndexes) {
            return currentIndexes.values()
                                 .stream()
                                 .flatMap(idx -> idx.packages.stream())
                                 .filter(p -> enclosingPackage.isEmpty() || p.startsWith(enclosingPackage + "."))
                                 .map(p -> {
                                     int dot = p.indexOf('.', enclosingPackage.length() + 1);
                                     return dot == (-1) ? p : p.substring(0, dot);
                                 })
                                 .distinct()
                                 .map(p -> createPackageElement(at, p))
                                 .collect(Collectors.toSet());
        }
    }

    private PackageElement createPackageElement(AnalyzeTask at, String packageName) {
        Names names = Names.instance(at.getContext());
        Symtab syms = Symtab.instance(at.getContext());
        PackageElement existing = syms.enterPackage(syms.unnamedModule, names.fromString(packageName));

        return existing;
    }

    private Element createArrayLengthSymbol(AnalyzeTask at, TypeMirror site) {
        Name length = Names.instance(at.getContext()).length;
        Type intType = Symtab.instance(at.getContext()).intType;

        return new VarSymbol(Flags.PUBLIC | Flags.FINAL, length, intType, ((Type) site).tsym);
    }

    private Element createDotClassSymbol(AnalyzeTask at, TypeMirror site) {
        Name _class = Names.instance(at.getContext())._class;
        Type classType = Symtab.instance(at.getContext()).classType;
        Type erasedSite = (Type)at.getTypes().erasure(site);
        classType = new ClassType(classType.getEnclosingType(), com.sun.tools.javac.util.List.of(erasedSite), classType.asElement());

        return new VarSymbol(Flags.PUBLIC | Flags.STATIC | Flags.FINAL, _class, classType, erasedSite.tsym);
    }

    private Iterable<? extends Element> scopeContent(AnalyzeTask at, Scope scope, Function<Element, Iterable<? extends Element>> elementConvertor) {
        Iterable<Scope> scopeIterable = () -> new Iterator<Scope>() {
            private Scope currentScope = scope;
            @Override
            public boolean hasNext() {
                return currentScope != null;
            }
            @Override
            public Scope next() {
                if (!hasNext())
                    throw new NoSuchElementException();
                try {
                    return currentScope;
                } finally {
                    currentScope = currentScope.getEnclosingScope();
                }
            }
        };
        @SuppressWarnings("unchecked")
        List<Element> result = Util.stream(scopeIterable)
                             .flatMap(this::localElements)
                             .flatMap(el -> Util.stream((Iterable<Element>)elementConvertor.apply(el)))
                             .collect(toCollection(ArrayList :: new));
        result.addAll(listPackages(at, ""));
        return result;
    }

    private Stream<Element> localElements(Scope scope) {
        //workaround for: JDK-8024687
        Iterable<Element> elementsIt = () -> new Iterator<Element>() {
            Iterator<? extends Element> it = scope.getLocalElements().iterator();
            @Override
            public boolean hasNext() {
                while (true) {
                    try {
                        return it.hasNext();
                    } catch (CompletionFailure cf) {
                        //ignore...
                    }
                }
            }
            @Override
            public Element next() {
                while (true) {
                    try {
                        return it.next();
                    } catch (CompletionFailure cf) {
                        //ignore...
                    }
                }
            }
        };
        Stream<Element> elements = Util.stream(elementsIt);

        if (scope.getEnclosingScope() != null &&
            scope.getEnclosingClass() != scope.getEnclosingScope().getEnclosingClass()) {
            elements = Stream.concat(elements, scope.getEnclosingClass().getEnclosedElements().stream());
        }

        return elements;
    }

    @SuppressWarnings("fallthrough")
    private Iterable<TypeMirror> findTargetType(AnalyzeTask at, TreePath forPath) {
        if (forPath.getParentPath() == null)
            return null;

        Tree current = forPath.getLeaf();

        switch (forPath.getParentPath().getLeaf().getKind()) {
            case ASSIGNMENT: {
                AssignmentTree tree = (AssignmentTree) forPath.getParentPath().getLeaf();
                if (tree.getExpression() == current)
                    return Collections.singletonList(at.trees().getTypeMirror(new TreePath(forPath.getParentPath(), tree.getVariable())));
                break;
            }
            case VARIABLE: {
                VariableTree tree = (VariableTree) forPath.getParentPath().getLeaf();
                if (tree.getInitializer()== current)
                    return Collections.singletonList(at.trees().getTypeMirror(forPath.getParentPath()));
                break;
            }
            case ERRONEOUS:
                return findTargetType(at, forPath.getParentPath());
            case NEW_CLASS: {
                NewClassTree nct = (NewClassTree) forPath.getParentPath().getLeaf();
                List<TypeMirror> actuals = computeActualInvocationTypes(at, nct.getArguments(), forPath);

                if (actuals != null) {
                    Iterable<Pair<ExecutableElement, ExecutableType>> candidateConstructors = newClassCandidates(at, forPath.getParentPath());

                    return computeSmartTypesForExecutableType(at, candidateConstructors, actuals);
                } else {
                    return findTargetType(at, forPath.getParentPath());
                }
            }
            case METHOD:
                if (!isThrowsClause(forPath)) {
                    break;
                }
                // fall through
            case THROW:
                return Collections.singletonList(at.getElements().getTypeElement("java.lang.Throwable").asType());
            case METHOD_INVOCATION: {
                MethodInvocationTree mit = (MethodInvocationTree) forPath.getParentPath().getLeaf();
                List<TypeMirror> actuals = computeActualInvocationTypes(at, mit.getArguments(), forPath);

                if (actuals == null)
                    return null;

                Iterable<Pair<ExecutableElement, ExecutableType>> candidateMethods = methodCandidates(at, forPath.getParentPath());

                return computeSmartTypesForExecutableType(at, candidateMethods, actuals);
            }
        }

        return null;
    }

    private List<TypeMirror> computeActualInvocationTypes(AnalyzeTask at, List<? extends ExpressionTree> arguments, TreePath currentArgument) {
        if (currentArgument == null)
            return null;

        int paramIndex = arguments.indexOf(currentArgument.getLeaf());

        if (paramIndex == (-1))
            return null;

        List<TypeMirror> actuals = new ArrayList<>();

        for (ExpressionTree arg : arguments.subList(0, paramIndex)) {
            actuals.add(at.trees().getTypeMirror(new TreePath(currentArgument.getParentPath(), arg)));
        }

        return actuals;
    }

    private List<Pair<ExecutableElement, ExecutableType>> filterExecutableTypesByArguments(AnalyzeTask at, Iterable<Pair<ExecutableElement, ExecutableType>> candidateMethods, List<TypeMirror> precedingActualTypes) {
        List<Pair<ExecutableElement, ExecutableType>> candidate = new ArrayList<>();
        int paramIndex = precedingActualTypes.size();

        OUTER:
        for (Pair<ExecutableElement, ExecutableType> method : candidateMethods) {
            boolean varargInvocation = paramIndex >= method.snd.getParameterTypes().size();

            for (int i = 0; i < paramIndex; i++) {
                TypeMirror actual = precedingActualTypes.get(i);

                if (this.parameterType(method.fst, method.snd, i, !varargInvocation)
                        .noneMatch(formal -> at.getTypes().isAssignable(actual, formal))) {
                    continue OUTER;
                }
            }
            candidate.add(method);
        }

        return candidate;
    }

    private Stream<TypeMirror> parameterType(ExecutableElement method, ExecutableType methodType, int paramIndex, boolean allowVarArgsArray) {
        int paramCount = methodType.getParameterTypes().size();
        if (paramIndex >= paramCount && !method.isVarArgs())
            return Stream.empty();
        if (paramIndex < paramCount - 1 || !method.isVarArgs())
            return Stream.of(methodType.getParameterTypes().get(paramIndex));
        TypeMirror varargType = methodType.getParameterTypes().get(paramCount - 1);
        TypeMirror elemenType = ((ArrayType) varargType).getComponentType();
        if (paramIndex >= paramCount || !allowVarArgsArray)
            return Stream.of(elemenType);
        return Stream.of(varargType, elemenType);
    }

    private List<TypeMirror> computeSmartTypesForExecutableType(AnalyzeTask at, Iterable<Pair<ExecutableElement, ExecutableType>> candidateMethods, List<TypeMirror> precedingActualTypes) {
        List<TypeMirror> candidate = new ArrayList<>();
        int paramIndex = precedingActualTypes.size();

        this.filterExecutableTypesByArguments(at, candidateMethods, precedingActualTypes)
            .stream()
            .flatMap(method -> parameterType(method.fst, method.snd, paramIndex, true))
            .forEach(candidate::add);

        return candidate;
    }


    private TypeMirror resultTypeOf(Element el) {
        //TODO: should reflect the type of site!
        return switch (el.getKind()) {
            case METHOD -> ((ExecutableElement) el).getReturnType();
            // TODO: INSTANCE_INIT and STATIC_INIT should be filtered out
            case CONSTRUCTOR, INSTANCE_INIT, STATIC_INIT -> el.getEnclosingElement().asType();
            default -> el.asType();
        };
    }

    private void addScopeElements(AnalyzeTask at, Scope scope, Function<Element, Iterable<? extends Element>> elementConvertor, Predicate<Element> filter, Predicate<Element> smartFilter, List<Suggestion> result) {
        addElements(scopeContent(at, scope, elementConvertor), filter, smartFilter, result);
    }

    private Iterable<Pair<ExecutableElement, ExecutableType>> methodCandidates(AnalyzeTask at, TreePath invocation) {
        MethodInvocationTree mit = (MethodInvocationTree) invocation.getLeaf();
        ExpressionTree select = mit.getMethodSelect();
        List<Pair<ExecutableElement, ExecutableType>> result = new ArrayList<>();
        Predicate<Element> accessibility = createAccessibilityFilter(at, invocation);

        switch (select.getKind()) {
            case MEMBER_SELECT:
                MemberSelectTree mst = (MemberSelectTree) select;
                TreePath tp = new TreePath(new TreePath(invocation, select), mst.getExpression());
                TypeMirror site = at.trees().getTypeMirror(tp);

                if (site == null || site.getKind() != TypeKind.DECLARED)
                    break;

                Element siteEl = at.getTypes().asElement(site);

                if (siteEl == null)
                    break;

                if (isStaticContext(at, tp)) {
                    accessibility = accessibility.and(STATIC_ONLY);
                }

                for (ExecutableElement ee : ElementFilter.methodsIn(membersOf(at, siteEl.asType(), false))) {
                    if (ee.getSimpleName().contentEquals(mst.getIdentifier())) {
                        if (accessibility.test(ee)) {
                            result.add(Pair.of(ee, (ExecutableType) at.getTypes().asMemberOf((DeclaredType) site, ee)));
                        }
                    }
                }
                break;
            case IDENTIFIER:
                IdentifierTree it = (IdentifierTree) select;
                for (ExecutableElement ee : ElementFilter.methodsIn(scopeContent(at, at.trees().getScope(invocation), IDENTITY))) {
                    if (ee.getSimpleName().contentEquals(it.getName())) {
                        if (accessibility.test(ee)) {
                            result.add(Pair.of(ee, (ExecutableType) ee.asType())); //XXX: proper site
                        }
                    }
                }
                break;
            default:
                break;
        }

        return result;
    }

    private Iterable<Pair<ExecutableElement, ExecutableType>> newClassCandidates(AnalyzeTask at, TreePath newClassPath) {
        NewClassTree nct = (NewClassTree) newClassPath.getLeaf();
        Element type = at.trees().getElement(new TreePath(newClassPath.getParentPath(), nct.getIdentifier()));
        TypeMirror targetType = at.trees().getTypeMirror(newClassPath);
        if (targetType == null || targetType.getKind() != TypeKind.DECLARED) {
            Iterable<TypeMirror> targetTypes = findTargetType(at, newClassPath);
            if (targetTypes == null)
                targetTypes = Collections.emptyList();
            targetType =
                    StreamSupport.stream(targetTypes.spliterator(), false)
                                 .filter(t -> at.getTypes().asElement(t) == type)
                                 .findAny()
                                 .orElse(at.getTypes().erasure(type.asType()));
        }
        List<Pair<ExecutableElement, ExecutableType>> candidateConstructors = new ArrayList<>();
        Predicate<Element> accessibility = createAccessibilityFilter(at, newClassPath);

        if (targetType != null &&
            targetType.getKind() == TypeKind.DECLARED &&
            type != null &&
            (type.getKind().isClass() || type.getKind().isInterface())) {
            for (ExecutableElement constr : ElementFilter.constructorsIn(type.getEnclosedElements())) {
                if (accessibility.test(constr)) {
                    ExecutableType constrType =
                            (ExecutableType) at.getTypes().asMemberOf((DeclaredType) targetType, constr);
                    candidateConstructors.add(Pair.of(constr, constrType));
                }
            }
        }

        return candidateConstructors;
    }

    @Override
    public List<Documentation> documentation(String code, int cursor, boolean computeJavadoc) {
        suspendIndexing();
        try {
            return documentationImpl(code, cursor, computeJavadoc);
        } catch (Throwable exc) {
            proc.debug(exc, "Exception thrown in SourceCodeAnalysisImpl.documentation");
            return Collections.emptyList();
        } finally {
            resumeIndexing();
        }
    }

    //tweaked by tests to disable reading parameter names from classfiles so that tests using
    //JDK's classes are stable for both release and fastdebug builds:
    private final String[] keepParameterNames = new String[] {
        "-parameters"
    };

    private List<Documentation> documentationImpl(String code, int cursor, boolean computeJavadoc) {
        code = code.substring(0, cursor);
        if (code.trim().isEmpty()) { //TODO: comment handling
            code += ";";
        }

        if (guessKind(code) == Kind.IMPORT)
            return Collections.emptyList();

        OuterWrap codeWrap = proc.outerMap.wrapInTrialClass(Wrap.methodWrap(code));
        return proc.taskFactory.analyze(codeWrap, List.of(keepParameterNames), at -> {
            SourcePositions sp = at.trees().getSourcePositions();
            CompilationUnitTree topLevel = at.firstCuTree();
            TreePath tp = pathFor(topLevel, sp, codeWrap, cursor);

            if (tp == null)
                return Collections.emptyList();

            TreePath prevPath = null;
            while (tp != null && tp.getLeaf().getKind() != Kind.METHOD_INVOCATION &&
                   tp.getLeaf().getKind() != Kind.NEW_CLASS && tp.getLeaf().getKind() != Kind.IDENTIFIER &&
                   tp.getLeaf().getKind() != Kind.MEMBER_SELECT) {
                prevPath = tp;
                tp = tp.getParentPath();
            }

            if (tp == null)
                return Collections.emptyList();

            Stream<Element> elements;
            Iterable<Pair<ExecutableElement, ExecutableType>> candidates;
            List<? extends ExpressionTree> arguments;

            if (tp.getLeaf().getKind() == Kind.METHOD_INVOCATION || tp.getLeaf().getKind() == Kind.NEW_CLASS) {
                if (tp.getLeaf().getKind() == Kind.METHOD_INVOCATION) {
                    MethodInvocationTree mit = (MethodInvocationTree) tp.getLeaf();
                    candidates = methodCandidates(at, tp);
                    arguments = mit.getArguments();
                } else {
                    NewClassTree nct = (NewClassTree) tp.getLeaf();
                    candidates = newClassCandidates(at, tp);
                    arguments = nct.getArguments();
                }

                if (!isEmptyArgumentsContext(arguments)) {
                    List<TypeMirror> actuals = computeActualInvocationTypes(at, arguments, prevPath);
                    List<TypeMirror> fullActuals = actuals != null ? actuals : Collections.emptyList();

                    candidates =
                            this.filterExecutableTypesByArguments(at, candidates, fullActuals)
                                .stream()
                                .filter(method -> parameterType(method.fst, method.snd, fullActuals.size(), true).findAny().isPresent())
                                .toList();
                }

                elements = Util.stream(candidates).map(method -> method.fst);
            } else if (tp.getLeaf().getKind() == Kind.IDENTIFIER || tp.getLeaf().getKind() == Kind.MEMBER_SELECT) {
                Element el = at.trees().getElement(tp);

                if (el == null ||
                    el.asType().getKind() == TypeKind.ERROR ||
                    (el.getKind() == ElementKind.PACKAGE && el.getEnclosedElements().isEmpty())) {
                    //erroneous element:
                    return Collections.emptyList();
                }

                Predicate<Element> accessibility = createAccessibilityFilter(at, tp);

                if (!accessibility.test(el)) {
                    //not accessible
                    return Collections.emptyList();
                }

                elements = Stream.of(el);
            } else {
                return Collections.emptyList();
            }

            List<Documentation> result = Collections.emptyList();

            try (JavadocHelper helper = JavadocHelper.create(at.task, findSources())) {
                result = elements.map(el -> constructDocumentation(at, helper, el, computeJavadoc))
                                 .filter(Objects::nonNull)
                                 .toList();
            } catch (IOException ex) {
                proc.debug(ex, "JavadocHelper.close()");
            }

            return result;
        });
    }

    private Documentation constructDocumentation(AnalyzeTask at, JavadocHelper helper, Element el, boolean computeJavadoc) {
        String javadoc = null;
        try {
            if (hasSyntheticParameterNames(el)) {
                el = helper.getSourceElement(el);
            }
            if (computeJavadoc) {
                javadoc = helper.getResolvedDocComment(el);
            }
        } catch (IOException ex) {
            proc.debug(ex, "SourceCodeAnalysisImpl.element2String(..., " + el + ")");
        }
        String signature = Util.expunge(elementHeader(at, el, !hasSyntheticParameterNames(el), true));
        return new DocumentationImpl(signature,  javadoc);
    }

    public void close() {
        for (AutoCloseable closeable : closeables) {
            try {
                closeable.close();
            } catch (Exception ex) {
                proc.debug(ex, "SourceCodeAnalysisImpl.close()");
            }
        }
    }

    private static final class DocumentationImpl implements Documentation {

        private final String signature;
        private final String javadoc;

        public DocumentationImpl(String signature, String javadoc) {
            this.signature = signature;
            this.javadoc = javadoc;
        }

        @Override
        public String signature() {
            return signature;
        }

        @Override
        public String javadoc() {
            return javadoc;
        }

    }

    private boolean isEmptyArgumentsContext(List<? extends ExpressionTree> arguments) {
        if (arguments.size() == 1) {
            Tree firstArgument = arguments.get(0);
            return firstArgument.getKind() == Kind.ERRONEOUS;
        }
        return false;
    }

    private boolean hasSyntheticParameterNames(Element el) {
        if (el.getKind() != ElementKind.CONSTRUCTOR && el.getKind() != ElementKind.METHOD)
            return false;

        ExecutableElement ee = (ExecutableElement) el;

        if (ee.getParameters().isEmpty())
            return false;

        return ee.getParameters()
                 .stream()
                 .allMatch(param -> param.getSimpleName().toString().startsWith("arg"));
    }

    private static List<Path> availableSourcesOverride; //for tests
    private List<Path> availableSources;

    private List<Path> findSources() {
        if (availableSources != null) {
            return availableSources;
        }
        if (availableSourcesOverride != null) {
            return availableSources = availableSourcesOverride;
        }
        List<Path> result = new ArrayList<>();
        Path home = Paths.get(System.getProperty("java.home"));
        Path srcZip = home.resolve("lib").resolve("src.zip");
        if (!Files.isReadable(srcZip))
            srcZip = home.getParent().resolve("src.zip");
        if (Files.isReadable(srcZip)) {
            boolean keepOpen = false;
            FileSystem zipFO = null;

            try {
                zipFO = FileSystems.newFileSystem(srcZip, Collections.emptyMap());
                Path root = zipFO.getRootDirectories().iterator().next();

                if (Files.exists(root.resolve("java/lang/Object.java".replace("/", zipFO.getSeparator())))) {
                    //non-modular format:
                    result.add(srcZip);
                } else if (Files.exists(root.resolve("java.base/java/lang/Object.java".replace("/", zipFO.getSeparator())))) {
                    //modular format:
                    try (DirectoryStream<Path> ds = Files.newDirectoryStream(root)) {
                        for (Path p : ds) {
                            if (Files.isDirectory(p)) {
                                result.add(p);
                            }
                        }
                    }

                    keepOpen = true;
                }
            } catch (IOException ex) {
                proc.debug(ex, "SourceCodeAnalysisImpl.findSources()");
            } finally {
                if (zipFO != null) {
                    if (keepOpen) {
                        closeables.add(zipFO);
                    } else {
                        try {
                            zipFO.close();
                        } catch (IOException ex) {
                            proc.debug(ex, "SourceCodeAnalysisImpl.findSources()");
                        }
                    }
                }
            }
        }
        return availableSources = result;
    }

    private Element getOriginalEnclosingElement(Element el) {
        if (el instanceof Symbol s) el = s.baseSymbol();
        return el.getEnclosingElement();
    }

    private String elementHeader(AnalyzeTask at, Element el, boolean includeParameterNames, boolean useFQN) {
        switch (el.getKind()) {
            case ANNOTATION_TYPE: case CLASS: case ENUM: case INTERFACE, RECORD: {
                TypeElement type = (TypeElement)el;
                String fullname = type.getQualifiedName().toString();
                Element pkg = at.getElements().getPackageOf(el);
                String name = pkg == null || useFQN ? fullname :
                        proc.maps.fullClassNameAndPackageToClass(fullname, ((PackageElement)pkg).getQualifiedName().toString());
                String typeParameters = typeParametersOpt(at, type.getTypeParameters(), includeParameterNames);
                String recordParameters;

                if (el.getKind() == ElementKind.RECORD) {
                    StringBuilder params = new StringBuilder();
                    String sep = "";

                    params.append("(");

                    for (RecordComponentElement component : type.getRecordComponents()) {
                        params.append(sep);
                        params.append(component.asType());
                        params.append(" ");
                        params.append(component.getSimpleName());
                        sep = ", ";
                    }

                    params.append(")");

                    recordParameters = params.toString();
                } else {
                    recordParameters = "";
                }

                return name + typeParameters + recordParameters;
            }

            case TYPE_PARAMETER: {
                TypeParameterElement tp = (TypeParameterElement)el;
                String name = tp.getSimpleName().toString();

                List<? extends TypeMirror> bounds = tp.getBounds();
                boolean boundIsObject = bounds.isEmpty() ||
                        bounds.size() == 1 && at.getTypes().isSameType(bounds.get(0), Symtab.instance(at.getContext()).objectType);

                return boundIsObject
                        ? name
                        : name + " extends " + bounds.stream()
                                .map(bound -> printType(at, proc, bound))
                                .collect(joining(" & "));
            }
            case FIELD:
                return appendDot(elementHeader(at, getOriginalEnclosingElement(el), includeParameterNames, false)) + el.getSimpleName() + ":" + el.asType();
            case ENUM_CONSTANT:
                return appendDot(elementHeader(at, getOriginalEnclosingElement(el), includeParameterNames, false)) + el.getSimpleName();
            case EXCEPTION_PARAMETER: case LOCAL_VARIABLE: case PARAMETER: case RESOURCE_VARIABLE:
                return el.getSimpleName() + ":" + el.asType();
            case CONSTRUCTOR: case METHOD: {
                StringBuilder header = new StringBuilder();

                boolean isMethod = el.getKind() == ElementKind.METHOD;
                ExecutableElement method = (ExecutableElement) el;

                if (isMethod) {
                    // return type
                    header.append(printType(at, proc, method.getReturnType())).append(" ");
                } else {
                    // type parameters for the constructor
                    String typeParameters = typeParametersOpt(at, method.getTypeParameters(), includeParameterNames);
                    if (!typeParameters.isEmpty()) {
                        header.append(typeParameters).append(" ");
                    }
                }

                // receiver type
                String clazz = elementHeader(at, getOriginalEnclosingElement(el), includeParameterNames, false);
                header.append(clazz);

                if (isMethod) {
                    //method name with type parameters
                    (clazz.isEmpty() ? header : header.append("."))
                            .append(typeParametersOpt(at, method.getTypeParameters(), includeParameterNames))
                            .append(el.getSimpleName());
                }

                // arguments
                header.append("(");
                String sep = "";
                for (Iterator<? extends VariableElement> i = method.getParameters().iterator(); i.hasNext();) {
                    VariableElement p = i.next();
                    header.append(sep);
                    if (!i.hasNext() && method.isVarArgs()) {
                        header.append(printType(at, proc, unwrapArrayType(p.asType()))).append("...");
                    } else {
                        header.append(printType(at, proc, p.asType()));
                    }
                    if (includeParameterNames) {
                        header.append(" ");
                        header.append(p.getSimpleName());
                    }
                    sep = ", ";
                }
                header.append(")");

                // throws
                List<? extends TypeMirror> thrownTypes = method.getThrownTypes();
                if (!thrownTypes.isEmpty()) {
                    header.append(" throws ")
                            .append(thrownTypes.stream()
                                    .map(type -> printType(at, proc, type))
                                    .collect(joining(", ")));
                }
                return header.toString();
            }
            default:
                return el.toString();
        }
    }
    private String appendDot(String fqn) {
        return fqn.isEmpty() ? fqn : fqn + ".";
    }
    private TypeMirror unwrapArrayType(TypeMirror arrayType) {
        if (arrayType.getKind() == TypeKind.ARRAY) {
            return ((ArrayType)arrayType).getComponentType();
        }
        return arrayType;
    }
    private String typeParametersOpt(AnalyzeTask at, List<? extends TypeParameterElement> typeParameters, boolean includeParameterNames) {
        return typeParameters.isEmpty() ? ""
                : typeParameters.stream()
                        .map(tp -> elementHeader(at, tp, includeParameterNames, false))
                        .collect(joining(", ", "<", ">"));
    }

    @Override
    public String analyzeType(String code, int cursor) {
        switch (guessKind(code)) {
            case IMPORT: case METHOD: case CLASS: case ENUM: case RECORD:
            case INTERFACE: case ANNOTATION_TYPE: case VARIABLE:
                return null;
            default:
                break;
        }
        ExpressionInfo ei = ExpressionToTypeInfo.expressionInfo(code, proc);
        return (ei == null || !ei.isNonVoid)
                ? null
                : ei.typeName;
    }

    @Override
    public QualifiedNames listQualifiedNames(String code, int cursor) {
        String codeFin = code.substring(0, cursor);
        if (codeFin.trim().isEmpty()) {
            return new QualifiedNames(Collections.emptyList(), -1, true, false);
        }
        OuterWrap codeWrap;
        switch (guessKind(codeFin)) {
            case IMPORT:
                return new QualifiedNames(Collections.emptyList(), -1, true, false);
            case METHOD:
                codeWrap = proc.outerMap.wrapInTrialClass(Wrap.classMemberWrap(codeFin));
                break;
            default:
                codeWrap = proc.outerMap.wrapInTrialClass(Wrap.methodWrap(codeFin));
                break;
        }
        return proc.taskFactory.analyze(codeWrap, at -> {
            SourcePositions sp = at.trees().getSourcePositions();
            CompilationUnitTree topLevel = at.firstCuTree();
            TreePath tp = pathFor(topLevel, sp, codeWrap, codeFin.length());
            if (tp.getLeaf().getKind() != Kind.IDENTIFIER) {
                return new QualifiedNames(Collections.emptyList(), -1, true, false);
            }
            Scope scope = at.trees().getScope(tp);
            TypeMirror type = at.trees().getTypeMirror(tp);
            Element el = at.trees().getElement(tp);

            boolean erroneous = (type.getKind() == TypeKind.ERROR && el.getKind() == ElementKind.CLASS) ||
                                (el.getKind() == ElementKind.PACKAGE && el.getEnclosedElements().isEmpty());
            String simpleName = ((IdentifierTree) tp.getLeaf()).getName().toString();
            boolean upToDate;
            List<String> result;

            synchronized (currentIndexes) {
                upToDate = classpathVersion == indexVersion;
                result = currentIndexes.values()
                                       .stream()
                                       .flatMap(idx -> idx.classSimpleName2FQN.getOrDefault(simpleName,
                                                                                            Collections.emptyList()).stream())
                                       .distinct()
                                       .filter(fqn -> isAccessible(at, scope, fqn))
                                       .sorted()
                                       .toList();
            }

            return new QualifiedNames(result, simpleName.length(), upToDate, !erroneous);
        });
    }

    private boolean isAccessible(AnalyzeTask at, Scope scope, String fqn) {
        TypeElement type = at.getElements().getTypeElement(fqn);
        if (type == null)
            return false;
        return at.trees().isAccessible(scope, type);
    }

    //--------------------
    // classpath indexing:
    //--------------------

    //the indexing can be suspended when a more important task is running:
    private void waitIndexingNotSuspended() {
        boolean suspendedNotified = false;
        synchronized (suspendLock) {
            while (suspend > 0) {
                if (!suspendedNotified) {
                    suspendedNotified = true;
                }
                try {
                    suspendLock.wait();
                } catch (InterruptedException ex) {
                }
            }
        }
    }

    public void suspendIndexing() {
        synchronized (suspendLock) {
            suspend++;
        }
    }

    public void resumeIndexing() {
        synchronized (suspendLock) {
            if (--suspend == 0) {
                suspendLock.notifyAll();
            }
        }
    }

    //update indexes, either initially or after a classpath change:
    private void refreshIndexes(int version) {
        try {
            Collection<Path> paths = new ArrayList<>();
            MemoryFileManager fm = proc.taskFactory.fileManager();

            appendPaths(fm, StandardLocation.PLATFORM_CLASS_PATH, paths);
            appendPaths(fm, StandardLocation.CLASS_PATH, paths);
            appendPaths(fm, StandardLocation.SOURCE_PATH, paths);

            Map<Path, ClassIndex> newIndexes = new HashMap<>();

            //setup existing/last known data:
            for (Path p : paths) {
                ClassIndex index = PATH_TO_INDEX.get(p);
                if (index != null) {
                    newIndexes.put(p, index);
                }
            }

            synchronized (currentIndexes) {
                //temporary setting old data:
                currentIndexes.clear();
                currentIndexes.putAll(newIndexes);
            }

            //update/compute the indexes if needed:
            for (Path p : paths) {
                waitIndexingNotSuspended();

                ClassIndex index = indexForPath(p);
                newIndexes.put(p, index);
            }

            synchronized (currentIndexes) {
                currentIndexes.clear();
                currentIndexes.putAll(newIndexes);
            }
        } catch (Exception ex) {
            proc.debug(ex, "SourceCodeAnalysisImpl.refreshIndexes(" + version + ")");
        } finally {
            synchronized (currentIndexes) {
                indexVersion = version;
            }
        }
    }

    private void appendPaths(MemoryFileManager fm, Location loc, Collection<Path> paths) {
        Iterable<? extends Path> locationPaths = fm.getLocationAsPaths(loc);
        if (locationPaths == null)
            return ;
        for (Path path : locationPaths) {
            if (".".equals(path.toString())) {
                //skip CWD
                continue;
            }

            paths.add(path);
        }
    }

    //create/update index a given JavaFileManager entry (which may be a JDK installation, a jar/zip file or a directory):
    //if an index exists for the given entry, the existing index is kept unless the timestamp is modified
    private ClassIndex indexForPath(Path path) {
        if (isJRTMarkerFile(path)) {
            FileSystem jrtfs = FileSystems.getFileSystem(URI.create("jrt:/"));
            Path modules = jrtfs.getPath("modules");
            return PATH_TO_INDEX.compute(path, (p, index) -> {
                try {
                    long lastModified = Files.getLastModifiedTime(modules).toMillis();
                    if (index == null || index.timestamp != lastModified) {
                        try (DirectoryStream<Path> stream = Files.newDirectoryStream(modules)) {
                            index = doIndex(lastModified, path, stream);
                        }
                    }
                    return index;
                } catch (IOException ex) {
                    proc.debug(ex, "SourceCodeAnalysisImpl.indexesForPath(" + path.toString() + ")");
                    return new ClassIndex(-1, path, Collections.emptySet(), Collections.emptyMap());
                }
            });
        } else if (!Files.isDirectory(path)) {
            if (Files.exists(path)) {
                return PATH_TO_INDEX.compute(path, (p, index) -> {
                    try {
                        long lastModified = Files.getLastModifiedTime(p).toMillis();
                        if (index == null || index.timestamp != lastModified) {
                            ClassLoader cl = SourceCodeAnalysisImpl.class.getClassLoader();

                            try (FileSystem zip = FileSystems.newFileSystem(path, cl)) {
                                index = doIndex(lastModified, path, zip.getRootDirectories());
                            }
                        }
                        return index;
                    } catch (IOException ex) {
                        proc.debug(ex, "SourceCodeAnalysisImpl.indexesForPath(" + path.toString() + ")");
                        return new ClassIndex(-1, path, Collections.emptySet(), Collections.emptyMap());
                    }
                });
            } else {
                return new ClassIndex(-1, path, Collections.emptySet(), Collections.emptyMap());
            }
        } else {
            return PATH_TO_INDEX.compute(path, (p, index) -> {
                //no persistence for directories, as we cannot check timestamps:
                if (index == null) {
                    index = doIndex(-1, path, Arrays.asList(p));
                }
                return index;
            });
        }
    }

    static boolean isJRTMarkerFile(Path path) {
        return path.equals(Paths.get(System.getProperty("java.home"), "lib", "modules"));
    }

    //create an index based on the content of the given dirs; the original JavaFileManager entry is originalPath.
    private ClassIndex doIndex(long timestamp, Path originalPath, Iterable<? extends Path> dirs) {
        Set<String> packages = new HashSet<>();
        Map<String, Collection<String>> classSimpleName2FQN = new HashMap<>();

        for (Path d : dirs) {
            try {
                Files.walkFileTree(d, new FileVisitor<Path>() {
                    int depth;
                    @Override
                    public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
                        waitIndexingNotSuspended();
                        if (depth++ == 0)
                            return FileVisitResult.CONTINUE;
                        String dirName = dir.getFileName().toString();
                        String sep = dir.getFileSystem().getSeparator();
                        dirName = dirName.endsWith(sep) ? dirName.substring(0, dirName.length() - sep.length())
                                                        : dirName;
                        if (SourceVersion.isIdentifier(dirName))
                            return FileVisitResult.CONTINUE;
                        return FileVisitResult.SKIP_SUBTREE;
                    }
                    @Override
                    public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
                        waitIndexingNotSuspended();
                        if (file.getFileName().toString().endsWith(".class")) {
                            String relativePath = d.relativize(file).toString();
                            String binaryName = relativePath.substring(0, relativePath.length() - 6).replace('/', '.');
                            int packageDot = binaryName.lastIndexOf('.');
                            if (packageDot > (-1)) {
                                packages.add(binaryName.substring(0, packageDot));
                            }
                            String typeName = binaryName.replace('$', '.');
                            addClassName2Map(classSimpleName2FQN, typeName);
                        }
                        return FileVisitResult.CONTINUE;
                    }
                    @Override
                    public FileVisitResult visitFileFailed(Path file, IOException exc) throws IOException {
                        return FileVisitResult.CONTINUE;
                    }
                    @Override
                    public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
                        depth--;
                        return FileVisitResult.CONTINUE;
                    }
                });
            } catch (IOException ex) {
                proc.debug(ex, "doIndex(" + d.toString() + ")");
            }
        }

        return new ClassIndex(timestamp, originalPath, packages, classSimpleName2FQN);
    }

    private static void addClassName2Map(Map<String, Collection<String>> classSimpleName2FQN, String typeName) {
        int simpleNameDot = typeName.lastIndexOf('.');
        classSimpleName2FQN.computeIfAbsent(typeName.substring(simpleNameDot + 1), n -> new LinkedHashSet<>())
                           .add(typeName);
    }

    //holder for indexed data about a given path
    public static final class ClassIndex {
        public final long timestamp;
        public final Path forPath;
        public final Set<String> packages;
        public final Map<String, Collection<String>> classSimpleName2FQN;

        public ClassIndex(long timestamp, Path forPath, Set<String> packages, Map<String, Collection<String>> classSimpleName2FQN) {
            this.timestamp = timestamp;
            this.forPath = forPath;
            this.packages = packages;
            this.classSimpleName2FQN = classSimpleName2FQN;
        }

    }

    //for tests, to be able to wait until the indexing finishes:
    public void waitBackgroundTaskFinished() throws Exception {
        boolean upToDate;
        synchronized (currentIndexes) {
            upToDate = classpathVersion == indexVersion;
        }
        while (!upToDate) {
            INDEXER.submit(() -> {}).get();
            synchronized (currentIndexes) {
                upToDate = classpathVersion == indexVersion;
            }
        }
    }

    /**
     * A candidate for continuation of the given user's input.
     */
    private static class SuggestionImpl implements Suggestion {

        private final String continuation;
        private final boolean matchesType;

        /**
         * Create a {@code Suggestion} instance.
         *
         * @param continuation a candidate continuation of the user's input
         * @param matchesType does the candidate match the target type
         */
        public SuggestionImpl(String continuation, boolean matchesType) {
            this.continuation = continuation;
            this.matchesType = matchesType;
        }

        /**
         * The candidate continuation of the given user's input.
         *
         * @return the continuation string
         */
        @Override
        public String continuation() {
            return continuation;
        }

        /**
         * Indicates whether input continuation matches the target type and is thus
         * more likely to be the desired continuation. A matching continuation is
         * preferred.
         *
         * @return {@code true} if this suggested continuation matches the
         * target type; otherwise {@code false}
         */
        @Override
        public boolean matchesType() {
            return matchesType;
        }
    }

    /**
     * The result of {@code analyzeCompletion(String input)}.
     * Describes the completeness and position of the first snippet in the given input.
     */
    private static class CompletionInfoImpl implements CompletionInfo {

        private final Completeness completeness;
        private final String source;
        private final String remaining;

        CompletionInfoImpl(Completeness completeness, String source, String remaining) {
            this.completeness = completeness;
            this.source = source;
            this.remaining = remaining;
        }

        /**
         * The analyzed completeness of the input.
         *
         * @return an enum describing the completeness of the input string.
         */
        @Override
        public Completeness completeness() {
            return completeness;
        }

        /**
         * Input remaining after the complete part of the source.
         *
         * @return the portion of the input string that remains after the
         * complete Snippet
         */
        @Override
        public String remaining() {
            return remaining;
        }

        /**
         * Source code for the first Snippet of code input. For example, first
         * statement, or first method declaration. Trailing semicolons will be
         * added, as needed.
         *
         * @return the source of the first encountered Snippet
         */
        @Override
        public String source() {
            return source;
        }
    }

}
